The Einstein relation for the diffusivity-mobility ratio of the carriers in semiconductors (hereeafter referred to as DMR) is a very important one, since by being a thermo-dynamic relation this is independent of any scattering mechanisms and also since one can determine the diffusivity from this relation by knowing the mobility and vice-versa. besides, the simplest method of analyzing semiconductor devices taking into account the degeneracy of the bands is to use the DMR to express the performance at the device terminals and the switching speed in terms of carrier concentration.